Speed regulator with a plurality of operating modes

ABSTRACT

A speed control for motor vehicles having an input device for the input of a desired speed by the driver, and having a plurality of operating modes which are able to be activated in different speed ranges and differ in their functional scope. A decision unit is provided which automatically undertakes the switchover of the operating mode in the light of the actual speed of the vehicle.

FIELD OF THE INVENTION

The present invention relates to a speed control for motor vehicles.

BACKGROUND INFORMATION

Germany Patent Application No. DE 199 58 120 describes, an example of aspeed control which, on the one hand, is operable in a so-called ACCmode (adaptive cruise control) and, on the other hand, is operable in aso-called Stop and Go mode.

In the ACC mode, the speed of the vehicle is controlled to a desiredspeed selected by the driver, provided the roadway ahead of his ownvehicle is free or preceding vehicles are moving faster or are farenough ahead. A distance sensor, such as a radar sensor, permitsdetecting preceding vehicles and other obstacles on the driver's ownroadway, and, if necessary, adapting the speed in such a way that thevehicle traveling directly ahead may be followed at an appropriatesafety distance. The ACC mode is generally provided for travel onexpress highways or well-improved highways at well moving traffic, thatis, for traffic situations which are characterized by relatively lowdynamics and relatively large distances between vehicles. Under theseconditions, for recording the surrounding traffic field, it issufficient to have a long-range direction-finding radar havingcomparatively low depth resolution. The relative speed of the locatedobject is directly measurable with the aid of the Doppler effect. Inorder to avoid frequent faulty reactions of the system, in general onlymoving radar objects are considered as relevant target objects, since ingeneral it is not to be expected that standing obstacles are on theroadway. However, in traffic situations having higher dynamics, such asin slow-moving traffic or Stop and Go traffic, or even in city traffic,standing targets should be included in the evaluation. In addition,because of the generally shorter vehicle separation distances, an evenmore detailed recording and evaluation of the traffic is desirable. TheACC mode is not suitable for this traffic situation, and may thereforebe activated only if the speed of one's own vehicle is greater than acertain limiting speed, for instance, greater than 30 km/h.

On the other hand, the Stop and Go mode is provided for the lower speedrange, and offers functions which are not available in the ACC mode,particularly the function of automatic braking of one's own vehicle to astandstill, such as when driving up to the end of a traffic jam. Undercertain conditions, automatic driveaway is then possible again, when thepreceding vehicle is set in motion again. These conditions aresatisfied, for example, if one's own vehicle has stood still onlyrelatively briefly, and if the target object followed up to now, i.e.,the preceding vehicle, has steadily remained within the locating rangeof the distance sensor. Under different conditions, on the other hand,it may be expedient to deactivate the system entirely, or, upondriveaway of the preceding vehicle, just to emit a driveaway request tothe driver, and to leave the final decision up to the driver. For thebroadened functionality in Stop and Go mode, not only is the recordingof standing targets required, but generally also an additionalclose-range sensor system is desirable, such as one in the form of avideo system having electronic image evaluation, a close-range radar ora light-optical distance sensor for the close range, including the leftand right roadway edges, so that even suddenly appearing obstacles maybe recognized early. This more complex recording and evaluation of thetraffic surroundings, which is requisite for the Stop and Go mode, or atleast desirable, could, however, lead to faulty reactions at higherspeeds. For this reason, Stop and Go mode is activable only at speeds upto an upper borderline speed, for instance, up to 40 km/h.

In the overlap zone between the speed ranges for ACC and Stop and Go,thus between 30 and 40 km/h in the assumed example, both modes areactivable, and the selection of mode remains left to the driver. In theconventional systems, special mode selection keys are provided forselecting the operating mode, using which the driver is able to activateeither the ACC mode or the Stop and Go mode. The active participation ofthe driver in selecting the operating mode is regarded as beingmeaningful, because in this manner it is brought to the driver'sattention in which mode the system just happens to be, and whichfunctions of the cruise control are available. In that way, it isparticularly avoided that the driver erroneously assumes, when thevehicle ahead is standing still, that the cruise control is in a Stopand Go mode, and relies on the cruise control automatically to brake thevehicle to a standstill. However, some drivers feel that the necessityof selecting the operating mode themselves is an impairment of operatingconvenience, and the command keys needed for this purpose make theoperating system more muddled and requiring explanation.

SUMMARY

An example speed control according to the present invention, upon properconsideration of the safety aspects, offers the advantage of greateroperating convenience and greater clarity and plausibility of theoperating system.

The speed control according to the present invention is in a position ofautomatically undertaking the change in operating mode, provided thatthe conditions for this are given. Therefore, the driver is considerablyrelieved, and special command keys for the selection of the operatingmode may be omitted. The most important criterion for the decisionconcerning a mode change is the actual speed V of the vehicle. Forreasons of clarity, one should here regard as the actual speed the speedindicated to the driver on the tachometer.

In order to increase transparency, it may be preferred if the driver hasit pointed out to him by a suitable signal, such as an optical or anacoustical signal, that a mode change has taken place, and in which modethe speed control is now.

In one preferred example embodiment, the speed control has only two mainoperating modes, namely the ACC mode and a mode which is here denoted as“Stop & Roll” (S&R). The concept “Stop & Roll” refers to a mode whichfalls between the ACC mode and the Stop & Go mode discussed at thebeginning, with respect to the sensor system it requires and thecomplexity when it comes to evaluate the traffic environment. In theStop & Roll mode, as in the Stop & Go mode, automatic braking of thevehicle to a standstill is possible, but, because of the restrictedsensor system, this mode is not intended highly dynamic trafficsituations, of the kind one might encounter in city traffic.

In order to avoid frequent change of modes, it is expedient if theswitching takes place as a function of the actual speed in conjunctionwith a certain hysteresis. Thereby it is particularly achieved that thespeed control remains in the current mode if the speed lies within theoverlap region in which both operating modes are permitted.

In both main operational modes an override by operating the gas pedal ispossible, just as with usual speed controls of this sort. Theacceleration request input by the driver on the gas pedal then hasprecedence over the lesser setpoint acceleration calculated by the speedcontrol. Even in these override situations a change is possible betweenthe two main modes.

When the speed control has been deactivated, it can be reactivated bythe input of a desired speed. Preferably, there then follows thedecision whether the ACC mode or the Stop & Roll mode shall beactivated, as a function of whether the actual speed lies above or belowthe limiting speed for ACC.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the present invention is explained in detailin the following description and is shown in the following figures:

FIG. 1 shows a block diagram of a speed control.

FIG. 2 shows a diagram of speed ranges at which the various operatingmodes of the speed control are able to be activated.

FIG. 3 shows a diagram for explaining the transitions between thevarious main operating modes and conditions of the speed control.

DETAILED DESCRIPTION OF AN EXAMPLE EMBODIMENT

In FIG. 1, a speed control 10 is shown as a block diagram by which, in amanner that is conventional but not described in greater detail here,the speed of a motor vehicle is controlled to a desired speed selectedby the driver. To operate speed control 10, a multifunctional lever isprovided on the steering wheel, which fulfills the functions of severalfunction keys: a “+” key 12 to activate the control and for raising thedesired speed V_(set), for example, in steps of 10 km/h, a “−” key 14for activating the control and for reducing desired speed V_(set), anOFF key 16 for deactivating the control and a resume key 18 for renewedactivation of the control, while assuming the desired speed prevailingbefore the last deactivation. In response to the first activation of thecontrol with the aid of the “+” key or “−” key, the actual speed V ofthe vehicle rounded up or down to the next full 10 is assumed as thedesired speed V_(set) of the vehicle, just as it is indicated on thetachometer. When resume key 18 is pressed, without a desired speedhaving been stored, for the determination of the desired speed, onerounds up or down to the nearest whole ten that deviates the least fromthe actual speed.

Speed control 10 takes up signals from a long range distance sensor 20,such as a long range radar and from a short range sensor system 22,which is formed, for example, by a short range radar, a light-opticaldistance sensor system, a video system and the like. When the sensorsystem detects a preceding vehicle traveling in one's own lane, ifnecessary, the speed of the vehicle is reduced to below the desiredspeed set, so that the preceding vehicle may be followed at anappropriate safety distance, for instance, at a selectable time gap of 1to 2 seconds. In one operating mode, known as ACC (adaptive cruisecontrol), the spacing regulation takes place exclusively with the aid ofsignals of long range distance sensor 20, which has a locating rangesuch as 10 to 200 m. This operating mode is provided for travel onexpress highways and well constructed highways at flowing traffic, thatis, for traffic situations in which, in general, people travel atrelatively high speeds. In addition, speed control 10 has a control modewhich is designated as Stop & Roll (S&R) and is provided for trafficsituations having high traffic density and correspondingly low speed,such as for slow-moving traffic or traffic jam operation on expresshighways or regular highways. In this mode, signals of the short rangesensor system 22 are also evaluated, so that shorter vehicle spacing maybe detected more accurately. Whereas in the ACC mode only movableobjects are considered as relevant target objects, in the Stop & Rollmode other standing targets also have to be evaluated which are detectedby long range distance sensor 20 or by close range sensor system 22. Inaddition, close range sensor system 22 also has a greater locatingangular range, so that objects can also be detected which in the closerange are located on neighboring lanes or at the edge of the roadway.Hereby the system is put into a position of reacting in time to suddenlyappearing obstacles, such as vehicles suddenly swinging in from the sidelane.

The Stop & Roll mode has at least one controlling function which is notavailable in the ACC mode, in particular, a stop function by which thevehicle may be automatically braked to a standstill upon the approach toa standing obstacle.

The control functions in the two operating modes ACC and Stop & Roll areknown as such, and are therefore not described here in more detail.

Speed control 10 has a decision unit 24 which, in dependence upon therespective traffic situation, decides in which operating mode the speedcontrol is working. The criteria for these decisions will be explainedin more detail below.

If decision unit 24 has selected the ACC mode, this is indicated to thedriver by the lighting up of an indicator light 28 on the dashboard.Correspondingly, an indicator light 30 indicates the operating mode Stop& Roll. In addition, a loudspeaker 32 is provided, by the use of whichthe driver is made aware of a change in the operating mode by anacoustical signal.

In FIG. 2 the speed ranges are shown, in which the operating modes ACCand Stop & Roll (S&R) are able to be activated. Basically, the ACC modeis able to be activated when the actual speed V of the vehicle isgreater than a limiting speed V_(s). The S&R mode is able to beactivated when the actual speed of the vehicle is lower than a speedV_(s)+h. The speed range between Vs and V_(s)+h is consequently ahysteresis range, in which either the ACC mode or the S&R mode may beactive. As an example, let us assume that the limiting speed Vs is 30km/h and that the hysteresis interval h is 5 km/h.

FIG. 3 shows the various operating states of the speed control as wellas the most important transitions between them. The active operatingstates divide up into the main operating modes ACC and S&R.

In a state 32 “readiness”, the sensor systems and the evaluation andcontrol algorithms of speed control 10 are active, so that the trafficevents can be followed, but no control commands are given to the drivingor the braking system of the vehicle, so that the control over thevehicle remains with the driver. So long as the driver does not activelyinput a command to activate the speed control, the speed control remainsin the readiness state, as is symbolized by an arrow T1.

The speed control of the vehicle may be activated from V=0 by thedriver's operating “+” key 12, “−” key 14 or resume key 18. Decisionunit 24 then decides, in the light of the actual speed V at this moment,whether the speed control is changing into state 34 “ACC active” or intostate 36 “S&R active”. If actual speed V is greater than limiting speedVs, then upon the activation of each of the three keys 12, 14, 18,transition into state 34 “ACC active”, corresponding to arrow T2 in FIG.3, takes place. If, on the other hand, actual speed V is less than orequal to V_(s), transition into state 36 “S&R active” takes placeaccording to arrow T3. As a result, the ACC mode is able to be activatedonly when the speed of the vehicle is at least 30 km/h. Otherwise thecontrol goes over into the S&R mode.

In state 36 now the driver has two possibilities of accelerating thevehicle to above 30 km/h and of going over into ACC mode. On the onehand, the driver is able to select a greater desired speed, by single ormultiple operation of “+” key 12, and thereby to accelerate the vehicle.As soon as the actual speed V is greater than V_(s)+h in the exampleassumed, that is, at least 35 km/h, decision unit 24 brings about atransition into state 34, according to arrow T4. As an alternative tothat, the driver may operate the gas pedal in state 36, and thusoverride the S&R control function, so that, according to arrow T5, thecontrol goes over into state 38, “override S&R”. If the vehicle isaccelerated to more than V_(s)+h, there takes place, according to arrowT7, a transition into state 40 “override ACC”. If the driver now lets upthe gas pedal, according to arrow T8, transition takes place into state34 “ACC active”. In general, the driver will then select a new desiredspeed V_(set) which is greater than Vs.

The driver, of course, is able to override state 34 “ACC active” byoperating the gas pedal, so that he temporarily reaches state 40,according to arrow T9.

Arrow T10 in FIG. 3 describes the regular transition from ACC mode intoS&R mode, or, more accurately, the transition from state 34 into state36. This transition takes place as soon as the actual speed V is lessthan V_(s).

In exceptional cases, a transition from state 40 “override ACC” intostate 38 “override S&R” is also possible, as indicated by arrow T11.This transition takes place when the actual speed V decreases to belowV_(s) in spite of the operation of the gas pedal, e.g., when the driverhas decreased the desired speed to a value below Vs, but then, byoperating the gas pedal, assures that the vehicle decelerates moreslowly than is specified by the speed control.

From state 36 “S&R active” a transition into a state 42 “S&R stop” isalso possible, as symbolized by arrow T12. In state 42, speed control 10effects the automatic braking of the vehicle to a standstill.Subsequently, the speed control, according to arrow T13, goes over intoone of several start-up states (not shown) which determine whether therenewed starting up of the vehicle is controlled by speed control 10, iftraffic conditions permit it, or when the driver confirms acorresponding start-up request, or whether the start-up procedure iscontrolled by the driver himself. Details of these start-up proceduresare described in DE 199 58 520 A1.

The transition into state 42 according to arrow T12 takes place when, instate 36, the speed of the vehicle (the determining factor here is notthe indicated but the actually measured speed) has decreased to below athreshold value such as 2 to 4 km/h, e.g. when approaching a standingobstacle.

In each of the active states, speed control 10 can be deactivated if oneof several predefined events occurs. The most important of these eventsmay be the operation of OFF key 16 by the driver and the operation ofthe brake pedal by the driver. In FIG. 3, deactivation from state 36“S&R active” is shown by only an arrow T14. The speed control then runsthrough a transition state 44, in which the control commands given outto the drive and/or brake system are gradually driven back, so that ajerk-free transition and a correspondingly great riding comfort isachieved. From transition state 44, the speed control then goes intostate 32 “readiness” again, according to arrow T15. The desired speedprevailing before the deactivation remains stored, however, and iscalled up again when the driver operates resume key 18 in state 32.

For the sake of completeness, in FIG. 3, still two further states 46“ACC braking” and 48 “S&R braking” are shown, in which the speed controlcan only act upon the braking system of the vehicle, but not upon thedrive system. These states are reached when the parking brake isoperated in the ACC mode (state 34) or in the S&R mode (state 36), orwhen, in these modes, the electronic stability program (ESP) of thevehicle detects a lane condition having low frictional connection (e.g.an icy road). A transition is in that case only possible in thedirection from the ACC mode into the S&R mode, that is, from state 46into state 48, according to arrow T16, when the actual speed V is lessthan Vs. From state 48 then, according to arrow T17, braking to astandstill is possible again.

Whereas in the exemplary embodiment described here it was assumed thatthe desired speed is only able to be changed in intervals of 10 km/h,the present invention is applicable analogously also in the case ofspeed controls in which the desired speed may be changed steplessly orin smaller increments, such as at intervals of 1 km/h.

The conditions for the change between modes ACC and S&R are summarizedonce more in the following Table. TABLE activation ACC T2 V > V_(s) AND(+, − OR resume is activated) activation S&R T3 V ≦ V_(s) AND (+, − ORresume is activated) S&R after ACC T4, T7 V > V_(s) + h ACC after S&RT10, T11 V ≦ V_(s)

1-7. (cancelled).
 8. A speed control for a motor vehicle comprising: aninput device for input of a desired speed by a driver; a plurality ofoperating modes which are able to be activated in different speed rangesand differ in functional scope; and a decision unit configured toautomatically undertake a switchover of the operating mode as a functionof an actual speed of the vehicle.
 9. The speed control as recited inclaim 8, further comprising: a display device to display the operatingmode.
 10. The speed control as recited in claim 8, further comprising: asignal device configured to signal to the driver a change in theoperating mode.
 11. The speed control as recited in claim 8, wherein oneof the operating modes is an operating mode for higher vehicle speedsthat is able to be activated only above a limiting speed, and another ofthe operating modes is an operating mode for lower vehicle speeds whichhas a function for the automatic braking of the vehicle to a standstilland is able to be activated in a speed range whose upper limit is atleast equal to the limiting speed.
 12. The speed control as recited inclaim 11, further comprising: a decision unit configured toautomatically cause a change from the mode for higher speeds into themode for lower speeds when the actual speed of the vehicle is less thanthe limiting speed.
 13. The speed control as recited in claim 11,wherein the decision unit causes a change from the mode for lower speedsinto the mode for higher speeds when the actual speed is greater by hthan the limiting speed, where h is a nonnegative value.
 14. The speedcontrol as recited in claim 11, wherein the decision unit activates themode for greater speeds if, in response to the input of the desiredspeed the actual speed of the vehicle is greater than the limiting speedand the decision unit activates the mode for lower speeds if, inresponse to the input of the desired speed the actual speed of thevehicle is less than or equal to the limiting speed.